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THEORETICAL BIOLOGY 



a number of individuals, each one of which has a definite 

 supply of genes. Consequently, each species, as the sum of 

 all the individual organisms, has a definite treasure-store of 

 genes, which transcends in a greater or less degree that har- 

 boured by each individual. 



Now undoubtedly the number and the nature of the genes 

 in the individual is not left to chance, but is governed by a 

 fixed rule, to which we give the name of genotype. 



The question arises whether the species likewise has 

 a genotype, or whether the boundary of one species with 

 regard to others is decided by the possibility that, when too 

 large a number of deviating genes meet one another, an 

 individual capable of living can no longer be produced through 

 crossing, for external, physiological reasons. Have we here 

 a perpetual process of " trial and error " going on, which 

 sometimes succeeds and sometimes fails ? Or is the species 

 a whole which works in accordance with plan, and is held 

 together by a fixed rule ? If so, what is the nature of this 

 rule ? 



WHAT THE SPECIES DOES 



Merely from the circumstance that the process of genesis 

 in the organism produces, as though confident of its goal, a 

 functioning framework, we become convinced that we are 

 faced with control by a natural factor working to plan. If 

 the development stopped prematurely, or if an inefficient 

 embryo resulted, we would not be justified in coming to this 

 conclusion. A whole that is incapable of performance is 

 merely an object, it is not even an implement, and still less 

 is it an organism. 



This criterion may be applied to the idea of the subject 

 that we must make for ourselves. The species, and Men- 

 delism confirms this, is not a mere classificatory formula 

 created by us in order that we may get a better view of the 



